Commercial-Off-the-Shelf (COTS) equipment is increasingly being used in military environments to take advantage of advancements in commercially available technology. By definition, COTS equipment has no or comparatively relaxed design environmental requirements. As a result, integration of the COTS equipment with systems designed to meet military specifications has proven to be difficult, especially for aircraft applications. A comprehensive solution to this integration challenge that accommodates all of the military operational requirements and FAA flight requirements has yet to be developed.
Such a solution would preferably allow for unforeseen variability in the COTS equipment and allow for quick, low cost integration of new equipment as it becomes available. Previously available attempts to solve these difficulties use unique equipment and are therefore expensive to modify even slightly. Without the unique equipment, however, it is difficult to efficiently provide the proper environment for the COTS equipment. Therefore the COTS equipment must be maintained in a mild environment while operating on military or even commercial aircraft. In addition to meeting the functional requirements for the equipment, the COTS equipment must also meet various requirements imposed by the relevant specifications for military applications and by the relevant Federal Aviation Administration (FAA) regulations for commercial applications. The various design requirements that the COTS equipment must meet include touch temperature, redundancy, smoke detection and clearing, fire suppression, thermal shock, vibration, electromagnetic interference, access, maintenance, redundancy. All of these requirements are preferably integrated into a comprehensive design approach that accommodates each potential piece of COTS equipment that might one day reside on the aircraft. However, the main parameters that are typically controlled are temperature and humidity.
Temperature control is typically accomplished by the aircraft environmental control system (ECS) which provides a source of air that has been conditioned to a pre-selected temperature. The cooling air is ducted to the various pieces of equipment or to the equipment cabinets or racks in which they are frequently located. From the equipment, or cabinets, the warmed exhaust air is then returned to the ECS system for re-cooling and recirculation. Because COTS equipment typically has very low limits on its air exhaust temperature COTS equipment is inefficient to cool. The low cooling efficiency in turn leads to very high cooling air flow demands (and therefore fan power consumption). The low temperature differential also makes transferring the heat off the plane very difficult. Additionally, changing the ducting configuration within a cabinet is costly and may involve changes to the configuration of the overall ECS system to accommodate even a single new piece of COTS equipment.
In addition to temperature control, humidity control can also be a challenge because many aircraft ground operations are conducted in humid environments with the cabin doors open. In such situations, elevated external ambient temperatures can limit cooling capacity while excessive humidity can cause moisture and condensation to be present in the aircraft. By way of contrast, in flight, the air is sometimes too dry for optimal performance of the COTS equipment. Unfortunately, a humidification system with the capacity to control the humidity for all of the equipment onboard a typical aircraft is prohibitively heavy.